Solvent extraction of mineral oils



Sept. 25, 1945. o.` L. PoLLY Erm.

SOLVENT EXTRACTION 0F MINERAL OILS Filed Aug. 14,l 1942 Patented Sept. 25, 1945 2,385,645 sonvENm Ex'ntAjcTIoN oF ivnNEaAi.. ons.

Orville L..Pmlly. Long, Beach, and Alva C. Byrns, Palos Verdes. Estates, Calif., assignors to Union Oil Company o.,C`alifo1"na, a corporation o fjCaliforna Los Angeles, Calif.,

Amilicatiimy Augustv 14, 1942., seriaiNd. 454,158.

13 claims.

This: invention relates to the refining' treat'-l ment' of"hydrocarhon` fractions andI has as one of? its objectives removing sulfur compoundsiirom petroleumy or coal tar oils and' distillatesjbr rainates" and extracts'- obtained from such ma;V terials by extraction with liquid sulfur dioxide or other solvents'commonto the art. More specically, the invention isa process for preferentially extracting sulfur compounds and/or aromatic hydrocarbons from oils which are predominantly olenic, paraiiinic or naphthenic and subsequently recov'eringthe solvent and extracted oil.

The invention is for the fractionation o f min-V eral oil with a new solvent Iwhichpermitsthe separation of A sulfur compounds and arom-atics from olens, parafns'an'dna'phthenes. 'Ph-escl'- vent is practically inert chemicallyand'itsv solvent power is readily controlled by addition or removal oi water.

The current art of solvent extraction is toward purifying 'hydrocarbon oils by the removal of undesirable constituents rather than to Athe resolution of hydrocarbon systems'into their typ"- ical components with al view to'rec'ove'r'ing intact the Various types of substances separated. Thus it is common practice to treat oils with sulfuric acid. A less drastic treatment may' be effected by the use of the lower alkylsulfonic'acids. In either case thel extract phase is neither readily nor completely convertibley to, regenerated solvent and unaltered extract oil. Crackeddistillates are particularly susceptible by Virtue of their high.v content otolensi, thiophenes and aromatics which tend'to be al'lcylated7 polymerized and sulfonated even at temperatures of 1 0 C. Thus large losses of solvent and oil occur, and the recovery ot valuable. sulfur bodies or, arcmatics is not feasible.

It is clearly an advantage to use a solvent Which-.is practically inert `chemically, the solvent powerjof .whichY can be readily adjusted and Whichj is easily recovered from the extractedv oil. We have found that compounds of the general type .in Whichone or more carboxyl groups are substituted for hydrogen inf` thio-ethers, such as alkylsuldes or thiophanes, are useful for preparing solvents with, the above-'mentioned desirable properties". More specifically,l we use ethyl thioglycolic acid and/or itsv homologsi ofV which i (c1. 26o-674') we prefer a mixture resulting from the acid'hydrolysis of the. neactionrproduct. of. methyl,` ethyl, propyl, butyl and amyl sodiomercaptides with sodiurn chloroacetate.

alkali liquors which liavebeen used tofrer'nove mercaptans from gasoline di'stillates. 'f' The ethyl thioglycolic acidrwhich We have proi duced'boils at about 123C. at l5 mm; pressure andrhasa speci'c gravity-'of- LMS' at 26 The' figure accompanying-thuis specificationdownwardly through column t it dissolves aporv tion o'the oil and eventually the'solventis with# drawn asthe'extractbase'via linefiu;

The railinate phase is withdrawn'irom column' I vvia4 line IlA and" is then 'mixed Witlr hotwat'er introduced through lineA I2'in inixer4 f3: From;

. mixerl3 the' raffinate to which'the hot'water has been added passesto separator Z'where'iti isaI-v lowed to separate intovtwo phases; `The upper phase comprising chiey rened raffinate is withdraws" from im@V system "tia 4une' '|55 Tue lower phaseA com'prising'mostfvof thesolvent'originally contained'fin'the fraction and the' water introduced v ia line l2 is withdrawn via line .l5 and is mixed Withfthe extractfphalse recovered from colunin l through lineflfin mixerI 4;. In the event that the rawstock introduced'intoline l0 is' a heavy material, suehras'lubricat'ing oil, it is` sometimes desirable to employ a iight desem to aidY in the yseparation of the solventfroml the extract. In this event the mixture Vfron@mixer 41 passes via line 2l, valve .22l and line 23` into mixer 49. where it is mxedwithlieht diIuent, such. as. petroleumV naphtha introduced .by `line l1.- From. mixer 49 themixture passesthrough line 24.into separator. Inseparator 8, themix.. ture separates into. twok phases, thevupper phase consists chiefly of. extract-.oil diluted with,V the light petroleum fraction.A Thisv phase is with,- drawn from separatorL il throughline125., From thel bottom of. separator-8 anl aqueousfsolution of the ethyl Y`thioglycolic wiet-fis,v withdrawn Such a mixture" of' sodio-1` mercaptides-is'usually-available as refinery Waste-y passed via line 29 into still 3.

, to sepeu'atev thiophenes from aromatics.

through line 26, valve 2'1 and line 28 and then By the aid of steam introduced into still 3 the extract oil' and Water are then passed overhead as a distillate through line 3l into condenser 32 where these vapors are condensed and passed as liquids into separator 4. From the bottom of separator 4 the Water is withdrawn through line 34 and discarded. From the top of separator 4 the extract oil is withdrawnrthrough line 33 and then may either be withdrawn completely from the sys`- tem via line 35 or, as an alternative, may be Ypassed by line 3B, valve 31 and lineV 38 to ref Theaqueous solution of sodium alkyl 'thiogly-Y colates in reactor 6 may be withdrawn throughl line 40, valve 4| and line 42 from the system or, as an alternative, this aoueous solution' may be diverted through Vvalve 44, line 43 into" mixer 45 where it is mixed-with sulfuric acid and then passed through separator 1.Y In the bottom of Yseparator 'l anaqueous solution of'sodium sulfate is withdrawnthroughf line 46 and is dis'- carded. The top layer in separator-"1. which is largely alkyl thioglycolic acid and contains some water, is passed through line 29 intojstill 3 whereY the water is distilled off through Yline 3l;

The substitutedthioglycolic acid recovered as Vthe bottom fraction in still 3 is withdrawn thereL from Vthrough line 30 and is passed through cooler k and thence through line 48 Yback toY the extraction column. Y

In the rabove description of the processwe.

. have described the 4auxiliaryidiluent introduced via line I1 into the 'mixture ofk extract oil :and

solvent in orderl YtoY obtain optimum separation' between the oil layer and the aqueous layer in Y separator 8. Inmany instances it-is unnecessary to use the auxiliary diluent to obtain proper phasefseparation between thewater and the ex-` tract oil and in Vthose cases we simply vclose valves' `22-and 21 and. open valve Y2!) to permit the mixture Yin mixerf41 to flow via line VI 9, valve Y 20 and line 29 directly into still 3 where thesolvent is separated from the Vextract Yoilin the manner described above. 5

Obviously,Y the extract oils or the vraflnates may be subiected kto a second stage ofextraction byV a repetitionyof the-procedure we have out.

lined, by employingl the solvent at Ythe same` or different concentrations.l ,Y Y TheV strength ofacid employed asjsolvent will vary with the particular` nature of. the fstock to beextracted. For example, it may be desirable W'e have found this tobe possible with our method,

Y butsuclfi av separation is more difcult thanV the with a preferred range of 50% to'90% acid by volume.Y In some cases it will be Yuseful to incorporate a third component in the aqueous acid employed as solvent. Thus we may use a polar substance mutually soluble in both the water and alkyl thioglycolic acid, as for example only, ethylene glycol or the sulfone oi' our substituted mercaptoacetic acid, in order to modify the selectivity of the solvent. Such addition imposes noY limitations on the procedure already proposed for operating our process.

As would be anticipated, loweringythe operating temperature improves the selectivity of our solvent. However, since the selectivity is readily adjusted by varying the acid concentration vwe prefer to operate the process simply at atmospheric temperature but we do not wish to imply any restriction to such temperature of 0D- eration. For example,where the extraction is being applied to a Wet stock, such as a gas oil distillate, it may be found advantageous to operate at a somewhatl higher temperature than Y atmospheric, to offset the eect of dilution of ceV separation VYoi' thiophenes `or `aroma/tics from `ole'-Y ns; In the'formercase we employ' a relatively Y Y,dilute acid., In any event' the'acid concentra- Z tion used would not be below? 40%.7'by volume,

the solvent. On the other hand, conditions may obtain where it is desired to employ substantially anhydrous alkyl thioglycolic acid at a temperature suiciently low to produce phase separation. Y Y

The action of this solvent, when` applied the treatment of olenic gasolines, is illustrated by the following examples, which in themselves are not intended to delineate or limit the general application of Vour process in any way.

ExAMrLEl I y A ml. sample ofl crackedY gasolinev of5l.3

VAPI and containing 3.46% sulfur was ,agitated two minutes with 50 inl. of a mixture ofv 80% ethyl thioglycolic acid in water Vat room temperature (about '70" F.) and allowed to settle two minutes. The extract was drawn off, treated` with water, and the extract oil recovered.

A second 100 ml. sample was treated twice consecutively with 50 ml. of 80% acid, as outlined above. Y e Y A third 100 ml. sample was treated three .times with 50 ml. portions of 80% acid, as above. The railinates'from each run` were washed with water until neutral and analyzed for sulfur. The results are presented in the following table;

Table I v Vollmtof volume weight weight Sorve t percent percent percent pefcqrl. yield of sulfur in sulfurexvglrlueranate raffinate tracted The rainates were improvedin colorand odor.

Y `A series ofrrbatchwise 'extractionsA similarto those above were made with `100 oa heavier cracked distillate of 41.2AA. P. -I. gravity Ycon-taining 3.6% sulfur.V At the end of Vthe sixth stage, using 50 ml. of 80% ethyl .thioglycolic'acid Yat each stage, the sulfurl content of` the,.w'ashed rainate was 2.57%, 21.5% ofthek oil hadl been 10.6 weight percent'sulfur.

' `removed as extract, for whichV an analysis showed f Aoideoncentration percent ethyl -thioglycolic acid in water l)' Percentncrease in vc]- Vuzne ofsolvent layer 2,5; dimethyl `thiophene 8 `16 26 100 Crude xylene 8 14 24 100 Cs thiophane 8 18 20` 60 v20 Di-sobutyleue 4 8 12` 22 Methyl cyclohexan 2 8 12 20 Purehexane 4 :8 l0 20 'The solubilities-:of the above substance fall into itwn Well dened classes; thiophenes, lthiophanes '25 and aromatics, versus ole'fns, naphthenes and paraflins `at each concentration of solvent. Greater specicity is `shown by the `more diluteY 'solvents 'The :inventiommay then be described as lresid- 30 ing iin the u-se of a =novel solvent for the separation' of 4oil into fractions. More specifically, the invention Imay be stated as vresiding in theuse of a `.mercapto-substituted carboxylic acidv containing :one or more carboxyl groups, as 'for e-x- `:35 ample, -the compound may -be a mercapto-substiytute'd mono carboxylic acid, =suoh as fbutyric or propionic acid or it may *be a'fmercaptoesubstituted poly carboxylic acid, such as succinic -acid or a'dipic acid. f

Furthermore, While /we ihave specifically shown that ethyl yt-hioglycolic racid and its Shomologs, :methyl propyl, Vbutyl and amyl thioglycolic -acids orimixtures thereof, -may1be`used, itis 'to be understood ythat We may 4also yuse thioglycolic acids '45 in which the -aIKylgrOupspeCied above may be substituted by varyl groupsoraralkyl groups.

-Our invention also embraces merc'apto-substituted carboxylic acids of the following type:

xo--Y-coon Where X1 and X2 are alkyl groups, unsaturated radicals derived trom alkyl groups by loss of hydrogen, aralkylgroups, hydrogen,`- carbocyclic rings, heterocyclic rings or RS groups the same or different from the RS- groups shown and where R represents an alkyl, aralkyl, carbocyclic or heterocyclic group, or an unsaturated radical derived from an alkyl group by loss of hydrogen and Y represents (CEE) n Where n=0 or an integer which may be as high as 5 or higher.

As a further modication of our invention We may add other materials to the alkyl thioglycolic acids to increase their selectivity, in addition to those disclosed above. A particularly suitable class oi addition compounds to be used is the salts of the substituted thioglycolic acids themselves. These salts may be obtained by partially neutralizing the substituted thioglycolic acid with the desired proportion of a suitable base, and may be used in conjunction with the previously disclosed modifying agents, such as Water. The bases which are suitable will include those of the alkali metals, ammonia, or :organic bases, such as the amines, di'arnines, .ethandlamines pyridine, morpholine, etc., `which are capable 4of producing salts. The advantages At'o :be .gained bythe .use of salts as addition ragents `is particularly marked `when it is desired to lproduce substantially pure aromatic hydrocarbons. Various hydrocarbon distillates are available 'Which may be fractionally distilled into a narrow boiling range such that .only one aromatic hydrocarbon is present to any .great extent. Then by selective solvent extraction by means fof our improved process it is possible to obtain the desired aromatic hydrocarbon in any desired degree of purity without the necessity for such auxiliar-y vpurifying methods as azeotropic distillation. In a similar Way our improved process may be employed in the extraction of narrow distillates containing thiophenes.

For example, in the extraction of toluene from a substrate oil Aof .low yaromatic content, such as gasoline rafiinate, aqueous ethyl mercaptoaceti'c acid does not permit theconcentration'of ytoluene beyond by volume of the totalloil Pin theextract layer. Above this concentration the system consists of only one phase. Therefore itis not possible to make pure -tolueneby extraction Ausing aqueous ethyl mercaptoacetic acid. However, the addition `of 20% by `Weight `ol ammonium ethyl mercaptcacetate to the .aqueous mercapto acid produces fa new solvent Which 'is :capable yof producing toluene of better than purity. This 4is shown by thedata lin the following tables, giving distribution Aratios for single stage eX- tractions:

A. Single stage extraction of ltoluene from gasoline raihnate (a) with a-solventconsisting 'of 60 weight vpercent .ethyl mercaptoacetic acid, 20 Weight percent ammonium ethyl mercaptoacetate, 20 Weight Apercent Water:

vPercent toluene feed Raffmate oil', Extract oil B. Single stage extraction of toluene from gasoline raiiinate1 `with a solvent consisting of 80 1 The gasoline raffinate -was `obmined vby low :temperature .sulfur dioxide extraction -of a California straightmun gasoline. weight percent ethyl lrnercaptoacetic acid, .20 Weightrpercent water:

P crcent toluene Iced Raflinate oily' 'F/ xtract c'il 2 Single phase system.

ample, in the extraction of butene-2 from other C4 hydrocarbons the urea, salt may be used in conjunction With. ethyl mercaptoacetic. acid either with or Without` the addition of Water.V

The following table lists the solubilities oi' butene-2 and butane in anhydrous ethyl mercaptoacetic acid with and without the addition of urea salt. The measurements were made un- Vder comparable conditions.

Butadiene is similar tobutene-Z in its solubility characteristics With these solvents.

Theabove is simply descriptive of the scope of Vour invention and is not to be understood as limiting the novel process and solvent which' we have discovered.

n This case is a continuation in part of our copending application, Serial No. 393,188, led May 13, 1941, now Patent No. 2,347,432.

We claim: Y Y 1. A process for the separation of a hydrocar- Y bon mixture into fractions of different Vtypes which Vcomprises extracting said mixture With a selective solvent Ycomprising a thioether in which at least one carboxylic acid 4group is substituted for a hydrogen atom, and a salt of said substituted thioether asia solvent modifying agent, thereby forming a Vrainate phase and an extract phase,

. and separating said phases.

2. A process Vfor the separation of a hydrocarbon mixture into fractions of diierent types which comprises extracting said mixture with a selective solvent thereby forming a ralinate phase and an extract phaser andV separating vsaid phases, said selective solvent comprising a carboxylic acid and a salt of 'said carboxylic acid, said carboxylic Aacid having the general formula Where X1 and X2 are alkyl groups, unsaturated radicals derived from alkyl groups by loss of hydrogen, aralkyl groups, hydrogen, carbocyclic ringsyheterocyclic Yrings or RSV groups the same or dierent from the RS group shown and Where R represents an alkyl, aralkyl, carbocyclic` or' heterocyclic group, or an unsaturated radical derived from an alkyl group by loss of hydrogen, and

Y'represents (CH2M Where 1t=0 or an integer.

3. A process according to claim 2 in which n is less than r3 vand R is an alkyl group containing between land 5 carbon atoms.

4. A process according to claim 2 in which the salt of the. carboxylic acid is an organic amine salt. Y

5. A process according to .claim 2 in which the salt of the'carboxylic acid is an alkali metal salt.

6. A process according to claim 2 in Which the hydrocarbon mixture also contains organic sulfur compounds and these are extracted by the selective solvent.

7. A process according to claim 2 in which the hydrocarbon mixture contains aromatic type hydrocarbons and these are extracted by the selective solvent.

8.l A process for the separation of a hydrocarbon mixture -into fractions of different types which comprises extracting said mixture with S- ethyl mercaptoacetic acid and ammonium S- ethyl mercaptoacetate.

9. A process as claimed in claim 8 in which Water isradded to the extraction agents.

10. A process for the separation-of a hydrocarbon mixture into fractions of different types which comprises extracting said mixture With S- ethyl mercaptoacetic acid and aurea salt thereof.

11. A process for the extraction of toluene from a Vhydrocarbon mixture Ycontaining toluene and non-aromatic hydrocarbons which comprises commingling said hydrocarbon mixture with a selective solvent comprising S-ethyl mercaptoacetic acid and ammonium S-ethyl mercaptoacetate and thereby forming a rafnate phase comprising hydrocarbon ractions'which are insoluble in the said selective solvent and an extract phase containing the toluene dissolved in the said selective solvent and separating said rafnate phase from said'extract phase. Y

12. A process for the recovery of toluene from a hydrocarbon mixture containing toluene'and nonaromatic hydrocarbons WhichA comprises contactingsaid mixture with a solvent comprising S-ethyl mercaptoacetic acid, ammonium S-ethyl mercaptoacetate and Water and therebydissolving Vthe toluene present in said hydrocarbon in said solvent, separating the vsolvent containing ,the dissolved'toluene from the remaining undissolved hydrocarbons and separating the toluene from the solvent.

13. A process according to claim l2 in which the solvent comprises about by Weight of S- Yethyl mercaptoacetic acid, Y20% by weight of am- Y monium S-'ethyl mercaptoacetateV and 20% Vrby weight of water.

' ORVILLE L. POLLY. ALVA C. BYRNS. Y 

